Regarding Miracle Man, Marvel owns the character completely as I recall.

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So they COULD bring him in to the MU, but with all the recent upheavals in the books and in management perhaps the plan has been put aside.

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Also there is the question: is he brought in as a new character, or is he shoehorned/retconned into continuity like Sentry, and Blue Marvel?

I would give him his own Earth. I don't think he works as a concept otherwise. They could do one event on Marvel's usual Earth where Miracle Man dominates the world but at the end of the event he would have to be kicked out. Otherwise no other stories could be told.